Best practices for archiving employees' mailboxes

Hi all,

Noob question here. I inherited administration of Entra and Exchange, and have had my first employee leaving the organisation.

My thinking is I need three things to happen:

1) Employee's mailbox is available for compliance purposes (it contains interactions with customers)

2) User no longer consumes licenses for Office 365

3) User's account doesn't hang around in Azure Entra, annoying me.

Anyone care to share best practices around what to do to meet these requirements, and in what order?

Thanks in advance,

Ben